For example, T2-weighted MRI can be used to differentiate between normal and diseased tissue in clinical studies of, e.g., the liver (see, e.g., Ohtomo K et al., Hepatocellular carcinoma and cavernous hemangioma: differentiation with MR imaging. Efficacy of T2 values at 0.35 and 1.5 T, Radiology 1988; 168 (3):621-623; Li W et al., Differentiation between hemangiomas and cysts of the liver with nonenhanced MR imaging: efficacy of T2 values at 1.5 T, Journal of Magnetic Resonance Imaging 1993:800-802; McFarland E G et al., Hepatic hemangiomas and malignant tumors: improved differentiation with heavily T2-weighted conventional spin-echo MR imaging, Radiology 1994; 193 (1):43-47; Ito K et al., Hepatic lesions: discrimination of nonsolid, benign lesions from solid, malignant lesions with heavily T2-weighted fast spin-echo MR imaging, Radiology 1997; 204 (3):729-737) and heart (see, e.g., Willerson J T et al., Abnormal myocardial fluid retention as an early manifestation of ischemic injury, American Journal of Pathology 1977; 87 (1):159-188; Higgins C B et al., Nuclear magnetic resonance imaging of acute myocardial infarction in dogs: alterations in magnetic relaxation times, American Journal of Cardiology 1983; 52 (1):184-188; Sekiguchi M et al., Histopathologic and ultrastructural observations of acute and convalescent myocarditis: a serial endomyocardial biopsy study, Heart & Vessels—Supplement 1985; 1:143-153; Sen-Chowdhry S et al., Arrhythmogenic right ventricular cardiomyopathy with fibrofatty atrophy, myocardial oedema, and aneurysmal dilation, Heart 2005; 91(6):784), as well as the brain and other organs. A widely exploited image contrast mechanism and/or process can include an alteration of water content by disease, with edematous tissue exhibiting a higher T2-weighted signal than normal tissue. Iron accumulation can provide another contrast mechanism/process, with excess iron resulting in a lower T2-weighted signal than normal tissue. Generally, a breath-hold fast spin-echo (FSE) pulse sequence (see, e.g., Hennig J et al., RARE imaging: a fast imaging method for clinical MR, Magnetic Resonance in Medicine 1986; 3 (6):823-833) has been used for clinical hepatic and myocardial T2-weighted MRI due to its higher data acquisition efficiency, as compared to a single spin-echo pulse sequence (see, e.g., Rydberg J N et al., Comparison of breath-hold fast spin-echo and conventional spin-echo pulse sequences for T2-weighted MR imaging of liver lesions, Radiology 1995; 194 (2):431-437; Simonetti O P et al., “Black blood” T2-weighted inversion-recovery MR imaging of the heart, Radiology 1996; 199 (1):49-57).
Quantitative tissue characterization by measurement of proton transverse relaxation rates (R2) can further improve the accuracy and precision of detecting pathological changes and assessing their severity. While a multiple single spin-echo pulse sequence with different echo time (TE) acquisitions may be considered as a reference technique for R2 measurement, this technique can be inefficient for clinical imaging. An alternative approach can be to employ a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence (see, e.g., Carr H et al., Effects of diffusion on free precession in nuclear magnetic resonance experiments, Physical Review 1954; 94 (3):630-638; Meiboom S et al., Modified spin-echo method for measuring nuclear relaxation times, The Review of Scientific Instruments 1958; 29 (8):688-691), and accelerate the corresponding multiple single spin echo data acquisitions by the echo train length. While a CPMG sequence can reduce the total imaging time of the corresponding multiple single spin-echo acquisitions with different echo times, its data acquisition efficiency can still be relatively insufficient for breath-hold imaging of the liver or heart. Accordingly, multiple single spin-echo and CPMG pulse sequences can generally be performed during free breathing with respiratory gating (see, e.g., St Pierre T G et al., Noninvasive measurement and imaging of liver iron concentrations using proton magnetic resonance, Blood 2005; 105(2):855-861; Voskaridou E et al., Magnetic resonance imaging in the evaluation of iron overload in patients with beta thalassaemia and sickle cell disease, British Journal of Haematology 2004; 126 (5):736-742; Alexopoulou E et al., R2 relaxometry with MRI for the quantification of tissue iron overload in beta-thalassemic patients, Journal of Magnetic Resonance Imaging 2006; 23 (2):163-170; Wood J C et al., MRI R2 and R2* mapping accurately estimates hepatic iron concentration in transfusion-dependent thalassemia and sickle cell disease patients, Blood 2005; 106(4):1460-1465), which can render them impractical for performing comprehensive assessment of the liver or heart within a clinically acceptable examination time, for example.
Different breath-hold spin-echo pulse sequences have recently been described for R2 measurement in the liver (see, e.g., Leoffler R et al., breath-hold technique for R2 quantification utilizing echo sharing for efficient sampling, In: Proceedings of the 15th Annual Meeting of ISMRM, Berlin, Germany, 2007) (Abstract 40). and heart (see, e.g., He T et al., Development of a novel optimized breathhold technique for myocardial T2 measurement in thalassemia, Journal of Magnetic Resonance Imaging 2006; 24 (3):580-585; He T, Kirk P et al., Multi-center transferability of a breath-hold T2 technique for myocardial iron assessment, Journal of Cardiovascular Magnetic Resonance 2008; 10 (1):11; Gouya H et al., Rapidly reversible myocardial edema in patients with acromegaly: assessment with ultrafast T2 mapping in a single-breath-hold MRI sequence, American Journal of Roentgenology 2008; 190 (6):1576-1582) with each sequence demonstrating potentially adequate image quality. Although these sequences may be considered as important developments, each can be subject to systematic errors in R2 measurement when compared with a CPMG pulse sequence, for example.
One of the objects of the present disclosure is to address and/or overcome at least some of the deficiencies as described herein above, and/or to overcome the exemplary deficiencies commonly associated with the prior art as, e.g., described herein. Another object of the present disclosure is to provide an exemplary embodiment of a breath-hold multi-echo FSE pulse sequence for accurate R2 measurement in the liver, heart, brain and other organs. Another object of the present disclosure is to compare such exemplary FSE pulse sequence with a navigator-gated CPMG pulse sequence. Yet another object of the present disclosure is to provide one or more relatively and/or sufficiently accurate exemplary non-invasive techniques and/or procedures for assessing tissue iron in disorders with iron overload and for monitoring the effectiveness of iron-chelating therapy in patients with transfusional iron overload, for example.